About: http://webisa.webdatacommons.org/441055173

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	Exact Cover Without explicitly saying anything about being planar or 4-regular or even a graph, perfect matching is a special case of the exact cover problem (as are sudoku, n-queens and many other problems).
http://www.w3.org/ns/prov#wasQuotedFrom	mathoverflow.net